A free space isolator (FSI) is a device configured to prevent optical beams from laser sources from being reflected within an optical subassembly in a manner that can damage major parts. As shown in FIG. 1, a conventional FSI 10 includes a sandwich type optical wafer and magnet 7, a 0-degree polarizer 1, a Faraday rotator 2, and a 45-degree polarizer 3. The difference between 0-degree and 45-degree polarizers can hardly be recognized by visual inspection, so one of the polarizers has a mark 6 formed by removing part of the edge. In general, the 0-degree polarizer works as an incident plane to polarize the incoming beam, the Faraday rotator is configured to rotate the incident beam, and the 45-degree polarizer can be utilized to transmit the rotated incident beam.
In the field of optical fiber communication, a laser beam 5 is converted from divergent light into collimated light by lens refraction before entering the FSI 10. In this process, the diameter of the laser beam 5 is relatively large on the incident plane 1 but relatively small on the outgoing plane 3. In this design, a buffer area for the incident laser beam 5 is formed by removing the size of the mark 6 from the edge of the outer diameter of the polarizer and then subtracting the size of the incident laser beam 5. That is, the remaining area is the buffer area for the laser beam 5.
The buffer area is very important for the laser beam. With regard to the laser beam, the wider the buffer area is, the better the effect will be. If the laser beam 5 deflects or reflects off a structure in the optical subassembly, it still can be kept in the buffer area, thereby preventing the laser beam 5 from deviating too far from the FSI 10. The size of the FSI 10 will go up if the buffer area is added under available conditions, resulting in a higher cost of the FSI.
This “Discussion of the Background” section is provided for background information only. The statements in this “Discussion of the Background” are not an admission that the subject matter disclosed in this “Discussion of the Background” section constitutes prior art to the present disclosure, and no part of this “Discussion of the Background” section may be used as an admission that any part of this application, including this “Discussion of the Background” section, constitutes prior art to the present disclosure.